WASHINGTON — A frantic day of legislative maneuvering ended in futility Tuesday for Speaker John A. Boehner, as the most conservative members of the House refused to back his proposed compromise to end the standoff over the federal budget.

The failure leaves a bipartisan Senate plan negotiated by Majority Leader Harry Reid (D-Nev.) and Minority Leader Mitch McConnell (R-Ky.) as the sole legislative way out of a stalemate that risks a U.S. default on its bills and huge economic disruptions. A bill that passed the Senate would receive Democratic support in the House, guaranteeing a majority if Boehner brings it to the floor.

Shortly after House leaders officially called off a vote on their most recent plan, spokesmen for Reid and McConnell said that Senate talks were resuming after a pause to allow Boehner (R-Ohio) a chance to get a bill through the House.

“Sen. Reid and Sen. McConnell have reengaged in negotiations and are optimistic that an agreement is within reach,” Reid spokesman Adam Jentleson said.

Michael Brumas, McConnell’s spokesman, said the two senators had “decided to work toward a solution.”

Earlier in the day, Fitch Ratings put the government’s AAA credit rating on watch for a potential downgrade because of the standoff. The company said it still believed the federal debt limit would be raised soon, but said the “political brinkmanship” was risking a default.

Treasury Department officials have said they will not be able to guarantee having enough money to pay all the government’s bills after Thursday, when it will be unable to borrow more. After that, “the Treasury would still have limited capacity to make payments,” Fitch said, but “it would be exposed to volatile revenue and expenditure flows.”

“The U.S. risks being forced to incur widespread delays of payments to suppliers and employees, as well as Social Security payments to citizens — all of which would damage the perception of U.S. sovereign creditworthiness and the economy,” the agency added.

Reid and White House officials sharply criticized Boehner’s plan during the course of the day. But despite the rhetoric, Boehner already had accepted the basic framework of the Senate deal. Behind the scenes, McConnell and Boehner worked to coordinate procedural steps that could allow a House-passed bill to rapidly be amended and move through the Senate.

Senators had indicated, however, that they would wait only a day to see whether the House could muster a majority.

White House Deputy Chief of Staff Rob Nabors, after a meeting in Reid’s office, said he wasn’t surprised to hear the House GOP plan had collapsed. “We were never really sure what they were up to,” he said.

In an interview with WABC-TV earlier in the day, President Obama said that White House officials had seen in the past that Boehner “can’t control his caucus.”

Boehner’s plan would have accepted key parts of the Senate deal — reopening the federal government by extending current spending levels through Jan. 15, and raising the nation’s debt limit through Feb. 7.

Some Senate Republicans portrayed the decision to wait for Boehner as an effort to save his influence and prevent the House from being dominated by its most ardent conservatives. Many Republican senators blame the conservatives in both chambers for having launched the party on a budget strategy that has failed.

In the end, however, the day’s maneuvers reinforced the sense that outside conservative groups now rival Boehner for influence in the House.

The speaker and his lieutenants had negotiated a plan with House members and scheduled a key procedural vote for early evening. Shortly before that could take place, Heritage Action, an influential conservative advocacy group, announced it would oppose the plan because it would not significantly roll back Obamacare, as the president's 2010 healthcare law is often called.

Within an hour, Boehner was forced to abandon the vote. Aides to the House leadership insisted, however, that the proposal was failing even before Heritage weighed in.

Republicans already had given up almost all of their demands for changes in the healthcare law or other shifts in government policy. With the government shutdown in its third week, the GOP has suffered badly in public opinion polls, and many lawmakers are ready to call a halt to a fight that began with conservatives seeking to use the leverage of a budget crisis to force Obama to make concessions.

“I can understand fighting for your cause, but there comes a point when you have an obligation to the country as a whole,” said Sen. Lindsey Graham (R-S.C.).

“The best thing for the country is for John Boehner to be able to deliver,” he said. “I just hope our colleagues in the House who believe it’s better to have more Republicans, not less, a governing majority, rather than a dysfunctional majority, will help John when he needs their help.”

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